1. Technical Field
The present disclosure relates to an antitheft device for vehicles, which prevents the vehicles from being thieved.
2. Related Art
An ignition key has conventionally been used to start an engine of automobile. The ignition key can readily be duplicated, and accordingly, there is a possibility that the automobile may be thieved using the duplicated ignition key. An immobilizer has been provided as an example of vehicle antitheft device which is used together with the ignition key. The immobilizer is a type of key using an electronically formed identification code and includes a subcode receiving unit and a code verification unit. The subcode receiving unit receives a subcode embedded in a transponder device provided in the ignition key. The code verification unit collates the subcode at the transponder side with a main code at the immobilizer side. As the result of collation, when the subcode corresponds with the main code, a normal ignition key is determined to be used, whereupon the automobile can be started. This prevents theft with the use of a duplicated ignition key.
However, a person who has illegally obtained a normal ignition key can easily thieve the automobile irrespective of an identification code of the immobilizer. Furthermore, a person who totally knows an electric system of the automobile closes an electric circuit around the ignition key to start the engine irrespective of provision of the vehicle antitheft device such as the above-mentioned ignition key or immobilizer.
In view of the foregoing problem, for example, Japanese Patent Application Publications JP-A-H01-56250 and JP-A-2000-38113 disclose vehicle antitheft devices both of which are provided with auxiliary input units using a keyboard, numerical keypads or a contactless IC card as well as the immobilizers, respectively. In each disclosed antitheft device, an auxiliary input operation such as input of a password is carried out in addition to a physical antitheft device and an electronic antitheft device both of which comprise the immobilizer.
However, when the auxiliary input unit as described above is used, an input terminal of the contactless IC card or a terminal device such as numerical keypads is installed at a place where the terminal or terminal device is easily visible for the purpose of easy input operation. Accordingly, there is a possibility that the terminal device may be disconnected from a circuit and the vehicle may be thieved by bypassing the auxiliary input unit.